Problem: Simplify the following expression: $k = \dfrac{10s^2 + 2s}{6ts - 8s} - \dfrac{8rs + 8s}{6ts - 8s}$ You can assume $r,s,t \neq 0$.
Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{10s^2 + 2s - (8rs + 8s)}{6ts - 8s}$ $k = \dfrac{10s^2 - 6s - 8rs}{6ts - 8s}$ The numerator and denominator have a common factor of $2s$, so we can simplify $k = \dfrac{5s - 3 - 4r}{3t - 4}$